The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicles typically include an internal combustion engine that combusts an air and fuel mixture in cylinders and thereby produces drive torque used to propel the vehicle. The engine may include pistons that reciprocate in the cylinders and that are coupled to a crankshaft. The pistons reciprocate in response to the combustion of the air and fuel mixture and thereby cause rotation of the crankshaft. The engine may further include a valve train that controls the flow of air into and out of the cylinders. The valve train may include a camshaft that selectively opens and closes intake valves and exhaust valves at the appropriate time and thereby controls the air flow. The camshaft may rotate with the crankshaft and thereby control the timing of the opening and closing relative to a position of the pistons within the cylinders. The valve train may further include a cam phaser coupled to the camshaft and the crankshaft. The cam phaser may adjust the rotational position of the camshaft with respect to the crankshaft and thereby adjust the timing of the opening and closing of the intake and exhaust valves relative to the position of the pistons.
Control systems have been developed to control engine operation, including engine shut down and starting. Stop-start engine control systems have been developed to increase fuel economy and reduce emissions. Stop-start systems selectively shut down and subsequently start the engine during periods of vehicle operation when drive torque from the engine is not required. For example, start-stop systems may shut down the engine as the vehicle slows to a stop when approaching a stop light. The start-stop systems may start the engine when a driver of the vehicle releases a brake pedal and/or depresses an accelerator pedal, indicating vehicle acceleration is desired. Accordingly, start-stop systems may frequently shut down and start the engine during vehicle operation based on inputs from the driver and/or various operating conditions, such as vehicle speed and engine speed.